This invention relates to a method and a machine for molding and more particularly relates to a method and machine for molding elongated and preferably generally cylindrical workpieces of a composite construction of plastic on a core. The invention herein has particular utility for the manufacture of rolls such as those used to condition may and which typically consist of a steel core with a resilient outer covering.
One well known process for molding parts of polyurethane is called reaction injection molding. In brief, the process consists of feeding isocynate and polyol from a mixing head into a mixer where they are mixed together just prior to injection of the mixture into the mold cavity. The mixture after curing forms the polyurethane part.
One known machine for the manufacture of workpieces such as conditioner rolls with a reaction injection molding process is comprised of four elongated mold segments which form a cylindrical mold cavity therebetween. One of the mold segments is fixed to a pivotable frame. A second and third of the mold quadrants are slidably movable (in a direction perpendicular to the mold axis) on the frame toward and away from the first quadrant between a mold closed and a mold open position. A fourth quadrant is mounted on the frame for linear movement toward and away from the first quadrant and is pivotable about an axis parallel to the mold cavity axis. The fourth quadrant is movable to a mold open position first by movement perpendicularly away from the first segment and then pivotal movement about an axis parallel to the mold axis. For movement to a mold closed position the foregoing movements are reversed.
The steps of operation of the machine are (1) load the workpiece into the open mold disposed with the mold cavity axis and all quadrants in a horizontal plane (2) move the second, third and fourth mold segments from a mold open to a mold closed condition (3) lock the mold segments together with clamps or latches (4) move the mold from a horizontal to a vertical position to ensure even filling of the mold cavity without air entrapment (5) fill the mold from the lower end with the reaction injection molding mixing head (6) return the mold to a horizontal position (7) open the mold latches (8) open mold segments and (9) remove completed roll. The prior art mold was found to be disadvantageous because it required repositioning or tipping of the entire mold from a horizontal to a vertical location. This disadvantage is typically found in molds for long thin parts or workpieces such as rolls which require filling in one position and unloading from the mold in another.
Accordingly, an object of this invention is to provide a machine for molding large elongated workpieces, the major components of which do not require substantial relocation during the steps of loading, molding and unloading a workpiece.
Another object of this invention is to provide a mold for elongated workpieces which has three of its four quadrants located in a vertical position and has its remaining quadrant movable between an inclined position for loading of the workpiece and a vertical position for closing of the mold.
Another object of this invention is to provide a mold with an improved runner system formed in an end plate of the cavity for uniformly channeling molding material into the mold cavity.